Individualized methods for physiologically adapted radiation therapy

The rapid development of different imaging modalities related to radiation therapy (RT) has largely affected the entire RT process from the planning phase of the treatment to the final treatment delivery. Treatment planning requires accurate anatomical information that can be provided by computed tomography (CT) and magnetic resonance imaging (MRI). Additional functional information about tissues and organs can be obtained by functional MRI or nuclear medicine imaging techniques such as single-photon emission tomography or positron emission tomography. The introduction of cone-beam computed tomography (CBCT) imaging to the RT delivery process has also opened new possibilities for RT treatment. In the past, mainly bony anatomy was visualized with planar imaging, which was used for the localization of the treatment. With CBCT also the prevailing soft tissue anatomy in addition to bones can be verified on a daily basis. By taking advantage of the growing amount of information obtainable by imaging, RT treatment plans can be customized further to suit the individual anatomical and physiological properties of patients. The focus of this thesis is on advanced methods for taking the individual variation in patients physiology into account during the RT treatment planning. Two particular cases of variation are investigated: bladder filling and deformation during the RT of urinary bladder cancer, and radiation-induced changes of salivary gland function related to the RT of head and neck cancer. In both cases, pre-treatment imaging is used to create a patient-specific model to estimate the changes that would take place during the RT. The aim is to take these predicted changes into account in the treatment planning process, with the goal of protecting normal tissues. At Helsinki University Central Hospital (HUCH), a method of adaptive radiation therapy (ART) was designed and clinically implemented for the treatment of urinary bladder cancer. In the applied workflow, four consecutive CT scans for RT treatment planning were used to capture the changes in bladder shape and size while the bladder was filling. Assuming that a similar bladder filling pattern applies during the course of RT, four treatment plans corresponding to the different bladder volumes were prepared and stored in a plan library. Before each treatment fraction a CBCT scan was performed. The treatment plan, which was the closest match to the bladder shape and size of the day, was selected from the library and delivered accordingly. The use of ART enabled better conformity of the treatment. It considerably reduced the absorbed dose to the intestinal cavity, as compared to the non-adaptive approach. Furthermore, the dose coverage in the urinary bladder was not compromised, while the treatment margins were substantially reduced. Overall, the method was found to be feasible, and it was rapidly taken into clinical practice. A model for predicting post-RT salivary flow was constructed and evaluated for the treatment of head and neck cancer. The model was based on pre-RT quantitative 99mTc-pertechnetate scintigraphy, direct measurement of total salivary flow and population-based dose-response behaviour. A good correlation was found between the modelled and the measured values of saliva flow rate. Hence, the model can be used as a predictive tool for risk-adapted treatment planning. One possible explanation for the remaining discrepancies between the predicted and the measured saliva flow rate values may be patients individual responses to radiation.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2016

Author dc:creator

• Tuomikoski, Laura

• lääketieteellinen fysiikka

Statement dc:rights

• Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
• This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
• Publikationen är skyddad av upphovsrätten. Den får läsas och skrivas ut för personligt bruk. Användning i kommersiellt syfte är förbjuden.

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/164961

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F164961